The Food and Drug Administration (FDA) recently cleared a number of cuffless blood pressure measurement devices, and the public’s response has been enthusiastic. On the surface, this sounds like a great thing. After all, more Americans ought to be keeping an eye on their blood pressure on a daily basis, and many people have adopted these wearables, which often look a lot like smartwatches.
But perhaps not surprisingly, almost all cuffless BP devices are not fully what they claim to be. At least not yet.
“Most people don't know that FDA clearance makes no representation of the accuracy of the device,” said Jordana B. Cohen, MD, MSCE, associate professor of medicine in the nephrology and hypertension division at the Hospital of the University of Pennsylvania.
When many people hear “FDA clearance,” they think “FDA approval,” but the latter only applies to products that have a significant risk of injury or illness, Dr. Cohen said.
All it takes for a manufacturer to get FDA clearance is to demonstrate that their product is "substantially equivalent to a legally marketed device,”—that is, one that is already FDA-cleared or -approved.
The only way to diagnose and monitor hypertension is through accurate BP measurement. But for many people, the measurements taken in a doctor’s office differ greatly from those taken at home.
Using validated home blood-pressure devices, patients can regularly monitor their blood pressure and report their measurements back to their physicians.
Dr. Cohen is also a member of the independent review committee for the US Blood Pressure Validated Device Listing (VDL™), available at validatebp.org. She recently wrote an article published on the website KevinMD about the benefits of validated BP measurement devices.
“A recent study in the Journal of Hypertension reported that out of the 100 best-selling blood pressure devices on Amazon, 81% had not undergone adequate clinical validation testing,” she wrote. “This means that potentially three in four patients working with their clinical teams to actively manage their blood pressure from home, and even some medical practices themselves, may not be getting accurate readings.”
The international organizations that issue the standards for blood pressure validation—including the Association for the Advancement of Medical Instrumentation and the American National Standards Institute—only very recently released the protocol for how to validate cuffless devices. To date, the VDL has validated more than 60 home, office, office automated, remote patient monitoring, ambulatory, kiosk and wrist devices.
But another big issue is that most of these devices—even if they have undergone any kind of immediate calibration against another valid device—are not being evaluated in real-world conditions.
“They are not being tested appropriately for the way people are actually using them, which is on the go, running around doing everyday tasks,” she said.
Studies published in JAMA Internal Medicine and elsewhere have shown that pulse oximetry devices, which measure oxygen levels in the blood, have widely varying results depending on patients’ skin color.
“This is the exact same technology used by cuffless blood pressure devices,” Dr. Cohen pointed out. “It extrapolates from the oxygen levels, and in people with darker skin tones, it misses if somebody has low oxygen levels in their blood at high rates.”
Dr. Cohen noted that the VDL is a living document.
When devices are ready, “we'll list them,” she said.